1. Field of the Invention
This invention relates to motorized film winding and rewinding devices for cameras, and more particularly to such device in which when rewinding of film is completed, the rewinding operation is automatically stopped.
2. Description of the Prior Art
In cameras in which winding up and rewinding of a film are carried out by an electric motor, in order that the electric motor be put into action to rewind the film it is the general practice that a control knob is operated to change over from the winding to the rewinding mode. Upon doing this, a rewinding operation is initiated. In such cameras, to terminate the rewinding operation, according to the prior art, the operator had to change over the aforesaid control knob to the winding mode again. That is, only when the operator is holding the control knob in the rewinding position, the electric motor acts to allow for rewinding of film. Then, when he removes his finger from pushing the control knob, this knob returns to the winding position where the motor is no longer energized. Alternatively, when the operator has moved the control knob to the rewinding position, the control knob is locked in that position, permitting the rewinding operation to continue going on by itself. Then, when the operator releases the control knob from the locking connection, the rewinding operation is terminated. With such conventional arrangements, however, as regards the former, the operator is obliged to sustain the depression of the control knob in the rewinding position for all the period of rewinding operation, thus suffering pain in his finger. Also in the latter case, when stopping the rewinding, the operator needs to take off the locking connection. Therefore, the operator must always take care in the progression of film rewinding, or it would result that even after all film has been rewound into the cartridge, the motor is still energized, causing premature consumption of the battery or heating of the camera. Further, such rewinding devices have an additional drawback that in order to inform the operator of when the rewinding of film comes to end, the complexity of camera structure has to be increased because it is required that the film counter be reversely rotated when the film is being rewound.
Attempts have been made to eliminate the abovedescribed drawbacks of such rewinding device by using a sensing member arranged upon setting of the rewinding mode to operate when the end of the film leader moves away from the takeup spool, or the root of the film tongue reaches the center of the length of the exposure aperture, so that the current supply to the motor is stopped, as illustrated in FIGS. 1 to 3. That is, this device is constructed with a cartridge 101 containing a film 102; sprocket 103; and a spool 104. And, the sensing member 105 is slidingly movable as it is guided by pins 108, and is urged by a spring 106 to abut with its end on the film 102. Positioned adjacent this sensing member 105 is a switch 107. In operating this device, when the film 102 reaches the position of FIG. 2, the sensing member 105 is allowed to slide in the direction of the arrow, wherein the switch 107 is turned off. Therefore, as illustrated in FIG. 3, the current supply to the motor 112 is cut off. Thus, motion of the motor is automatically stopped when the film has been rewound into the cartridge 101, leaving at least the film leader outside of the cartridge 101, and the film rewinding operation is also terminated. FIG. 3 shows an electrical power source or battery E; a switch 110 for controlling the current supply to the electric motor 112 when in the winding mode; and a switch 111 rendering it possible to supply current to the electric motor 112 when the back cover of the camera is open, or when the camera is not loaded with a film 112. However, such device has the following drawbacks. That is, since the sensing member is always pressed on the film surface, the flatness of the film is deteriorated badly. Also, since the sensing member is in frictional contact with the film when in the winding mode as well as in the rewinding mode, an increased load is laid on the electric motor. Further if this device were provided with no switches besides the switch cooperative with the sensing member, it would become impossible to supply current to the motor. Therefore, an additional switch which is closed when the back cover is open must be used as arranged in parallel with the sensing member switch. This calls for an increase in the complexity of the circuitry of the camera.
Also, to eliminate the drawbacks of such conventional device, upon consideration of the fact that the load which has been exerted on the film rewinding system as the film was being rewound lessens when the rewinding is completed, a device responsive to this lessening of the load for automatically stopping the rewinding operation has been proposed in U.S. Pat. No. 4,171,893 (issued Oct. 23, 1979). However, this device, because of its having such form that the drive gear rotating in response to driving torque transmitted from the motor is movable along its shaft of rotation to allow for release from the meshing engagement with a driven gear constituting part of a film rewinding system, is bound to employ expensive helical gears in coaxial relation to the drive gear. Otherwise, the drive gear could not be maintained in meshing engagement with the driven gear by the load exerted on the film rewinding system as the film is being rewound. That is, such device necessitates at least two helical gears which account for the increase in the production cost of the device.
Also in such device, while the helical gears are left engaged with each other, the control knob is operated to change over to the rewinding mode from the winding mode, so that the operator is given an unpleasant impression from the control knob. Further, to allow for movement of the drive gear along its shaft of rotation, the height of the camera must be disadvantageously increased from the value required for minimization of the bulk and size of the camera.